I am replacing my old carter YFA carb with a new one and i am very concerned with the outcome. i dont want to replace my carb with one that is going to have the same problems as mine or a different problem

Problems with my old YFA

• 10 in of vacuum at idle to the spark port- no adjustment fixed this ive tried for 3 years to adjust this out but no amount of troubleshooting will fix this.
• choke never worked right even after rebuilt replaced and adjusted
• unreliable, one day it floods another its gas starved
• all the screws are stripped from previous rebuilds
• it whistles like a train due to the top bracket being homemade by the previous owner.

my main concern is getting a new carb that still gets vacuum to the spark port at idle because right now im running my dist adv on the port midway up the carb body. if i run my dist advance on the spark port it will run my timing up to 20 BTDC and that will cause pinging at anything to far above idle. i even tried connecting the dist. advance to the spark port and backing off the timing to 10 BTDC but then i suffered a huge loss of power due to a slower timing curve.

https://www.ebay.com/itm/NEW-CARBURE...19.m1438.l2649

i would like a carb with a vacuum actuated choke like the one above, it will hopefully help with warm up and cold days

both of these have what i want but what are the possibilities that these will have vacuum to the spark port at idle? is that a common thing among carburetors or is my old one a special case?
if anyone has a YFA that also gets vacuum to their spark port or did get vacuum to the spark port please tell me how to remedy this situation. any advise is helpful. Thanks

 

The spark port is supposed to have a partial vacuum at the spark port, something less than manifold vacuum. This prevents a stumble when the throttle is opened on a accel, due to a rapidly falling vacuum signal if manifold vacuum instead of a ported signal being used. Is it possible somebody messed with your vacuum advance diaphragm setting, screwing out the diaphragm spring tension thus enabling a quicker advance?

 

as from what i understand i should set my timing 10 BTDC then connect the spark port (this will raise the idle speed due to the small advance in the timing) and as long as my carb and dist advance are working correctly and are adjusted right all i need to do is adjust initial timing.

 

If you're measuring vacuum from a timed "spark port" - that is, above the throttle butterflies - then by definition the RPM is "too high" and it's tipping in. There isn't any vacuum to be measured from a spark port at a factory idle, because it was developed or utilized for this very reason. No vacuum at idle.

Now if you instead connect the vacuum advance to a source of constant manifold vacuum - that is, below the throttle plates - then naturally there will be a lot of advance at idle. It won't be unusual to see 30° BTDC or more. This is no problem - at idle there is no load on the engine, and vacuum advance is strictly a load dependent device. As soon as the accelerator is depressed, the vacuum advance pulled in momentarily goes away. There are some advantages to a manifold connection- it keeps engine temperature esp. in stop & go down significantly.

If you're running into ping or engine knock connected to a manifold source, that is still a function of "total" timing adjustment or maybe a defective vacuum advance or something internal.

There is no difference in the way the vacuum advance works except at idle, when connected this way. Cruising at steady speeds on level ground there is no difference in vacuum levels. What it will do at idle is raise NOX levels - one reason Detroit de-tuned their engines to meet smog requirements in the 1970s. It is sometimes difficult to maintain a steady idle using a manifold source of vacuum - this is why "ported" vacuum advance has been utilized since the 1930s, and all kinds of solenoids and one way valves gee-gaws hanging off carburetors to complicate things.

The general rule is a stock-ish engine will run best using the ported or "timed" spark port. Modified engines, lumpy cams etc, benefit from a manifold connection. True racing engines have no vacuum advance at all, because they are tuned for wide open throttle, making it a moot point. A vacuum canister is just something else to fail so it is omitted entirely. If you drive on the street you want vacuum advance.

 

thanks tedster, that definately clears up some confusion about why some people prefer manifold vacuum over ported. the throttle blades on my carburetor or adjusted VERY closed to the point that it was a fairly low idle. no matter how i adjust the carb the vacuum to the spark port will never go below 8ish inches of vacuum.

i am still stuck on why my carb is getting vacuum to the spark port, adjustment doesnt it.

i tested my vac adv and its still good, adjustment could be off but the diagram is still good.

i would really like to know what other peoples Carter YFA's are running on the spark port, are they like mine or do they run 0 in of vacuum
also a picture of the spark port on a carter YFA is below tell me if im looking at the wrong port.

 

Are you certain that is a "timed" spark port? Or maybe some kind of hybrid? I dunno, that's why I ask.

If the port is plumbed above throttle plates the vacuum at idle should be Zero. Not 10", not 5", Zero. When accelerating, it should be Zero. Only when the load on the engine levels off, the vacuum starts to rise.

Wherever it is hooked up, it doesn't really matter. Set your base timing where you want it, though some experimentation is in order. Every engine is a bit different.

The key as always is to make the mechanical timing adjustments first, with the vacuum advance disconnected and plugged. This means running it up to 3k to 4k + RPM with a timing light and making sure the ignition timing advances and stops out where it should, moves smoothly up and down and returns smartly back to base setting. A few test drives are probably advised. When you are finally satisfied with the mechanical part of the ignition timing, then re-connect the vacuum advance.

Getting the vacuum advance adjusted properly is again kind of a cut and try process. What you don't do though, is touch your base timing, or mechanical advance. That's done with. When just the mechanical weights & distributor timing is dialed in right it will run pretty well.

Vacuum advance is mainly for improving steady level ground cruise performance & mileage, it will run noticeably smoother and have better driveability. But it is completely out of the picture whenever under hard acceleration, going up steep hills, etc.

 

well i checked my base timing last night and its fine, then i connected it to the spark port which raised the idle due to the advance of the timing, i retuned the carb to idle around the 700 rpm range. i drove it around a little and it has a part throttle bog that makes it really slow but there is no knocking pinging or anything like that. i floored it to make sure i wouldn't do anything weird and it was fine and it there were no acceleration issue. it runs better but there is still a bog in acceleration up a hill. i ordered a new carb yesterday, if that doesnt fix it i will know that there is another issue.

hopefully a new carb with an operating spark port will fix my problem.

 

It's been a long while since I had a Carter YF on my engine, but I recall there being 3 different vacuum ports on it. One was full manifold vacuum, one was the timed spark port, and the third was used by the EGR system. I didn't know enough about the systems at the time to really know what the differences were, but I wonder if that has something to do with it.

Either way, Tedster's writeup on the mechanical and base timing is a good one. Take care of those first. Vacuum advance is always supplementary, and you could actually just disconnect it and live without it as it's not *needed*. But, it's very nice to have.
I second disconnecting it for a while and getting your base and mechanical all dialed in. Then add the vacuum advance back in and get it set up. That'll separate the systems and let you focus on each one individually.

However, from what you have said above, it sounds like your carb has been gone through a number of times and who knows what's been mucked up or set wrong with it. A new carb might cure a LOT of headaches. Hopefully it does.

 

hopefully it does, im getting it around the 20th so until then i will try to locate which one is spark, egr and manifold. and find what i need to do with timing

 

sorry this thread is old but thought i would follow up with the results of my new carter YFA, everything works great now, no bog, the spark port works and it was very easy. sorry about pic quality but thanks to everybody for the help.

 

10 days is not old! (Stick around and you'll see some that are a couple years old resurface from time to time.)

To the contrary, it's much appreciated that you followed up and posted the results. Thank you.

Glad to hear it's running much better, that has to be a good relief.

 

Do you have plans to add an exhaust heat stove and duct it into the inlet snorkel?

 

no i took it off because becase it was rusted and when i bought it it had no vcv, i also dont know how to connect that valve on the air breather so that it will stay open when its fully warmed up

i fixed the rusted heat stove and i have the flex tube for connecting it but how does that vacuum system work with warm up and cold engines

 

Ford used a couple of systems to control the vacuum door on the snorkel.

A simple system is to run a vacuum hose connected to manifold vacuum to a TVS (Temperature / Vacuum Switch) screwed into the thermostat outlet neck. The door ducts heat into the snorkel - aiding cold engine driveability, hastening warm-up, and most importantly, preventing carb icing on cool, humid days. When the opening point temperature of the TVS is reached as the thermostat opens the vacuum port will switch open to bleed off vacuum, closing the door.

The second system is similar to the first except that it incorporates an additional temperature sensor that bleeds off vacuum signal proportionately with incoming air temp, holding it steady.

 

i have no tvs nore a place for one so i was unsure of the way to make or fabricate a TVS into my system